Dietary supplementation with bacteriophages or acidifiers mitigates Salmonella Enteritidis challenge effects in broilers by altering intestinal bacterial populations and morphology

The increasing prevalence of antibiotic resistance in the poultry industry necessitates the development of alternative strategies to control bacterial diseases such as salmonellosis caused by Salmonella Enteritidis ( S. Enteritidis). This study evaluated the effects of dietary bacteriophage and acidifier supplementation on growth performance, immune response, gut microbiota, intestinal morphology, and meat quality in broilers challenged with S. Enteritidis . A total of 700 one-day-old Ross 308 male chicks were randomly allocated to five dietary treatments in a completely randomized design with seven replicates of 20 birds each: a non-challenged negative control (CON), a Salmonella Enteritidis -challenged positive control (PC), and three additional challenged groups receiving diets supplemented with enrofloxacin, bacteriophage, or acidifier. On day 13, all groups except CON were orally challenged with S. Enteritidis (1 × 10⁸ CFU/mL). Salmonella infection markedly impaired feed intake, body weight, feed efficiency, and breast meat quality compared with the CON group (P < 0.05). Supplementation with bacteriophage or acidifier significantly alleviated these negative effects and reduced malondialdehyde levels (P < 0.05), while also increasing the activities of plasma antioxidant enzymes, including glutathione peroxidase and superoxide dismutase, compared with the challenged control group. Bacteriophage supplementation restored duodenal villus height and crypt depth and maintained cecal pH close to control values (P < 0.05). Quantitative PCR indicated higher populations of Lactobacillus and Bifidobacterium and reduced Salmonella spp. in the cecum. Overall, bacteriophage supplementation mitigated the detrimental effects of S. Enteritidis by improving gut health, antioxidant status, and meat quality, highlighting its potential to enhance poultry health and productivity in antibiotic-free production systems.